If I'm typing a tweet in Mountain Lion's new Notification Center panel, is there a way to send the tweet without moving my hands to the trackpad to click the "send" button? I've tried return, enter, ⌘return, and other key combinations, but nothing obvious sends the message.

In the process of trying to find an answer to this question I accidentally found a way to break the "Click to Tweet" button. I typed something in the tweet composer and then hit Esc, then the OS seemed to hang for a minute before closing Notification Center. Now I can click on the "Click to Tweet" button and it registers the click but the composer doesn't open. So, caution: don't try that combo if you care about tweeting.
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TortillaJul 27 '12 at 7:48

I've managed to do that several times tonight. In Terminal, you can reset Notification Center with a killall NotificationCenter; open /System/Library/CoreServices/Notification\ Center.app/
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Daniel♦Jul 27 '12 at 7:54